As is well known to those skilled in the art, it is possible to remove water from mixtures thereof with organic liquids by various techniques including adsorption or distillation. These conventional processes, particularly distillation, are however, characterized by high capital cost. In the case of distillation for example, the process requires expensive distillation towers, heaters, heat exchangers (reboilers, condensers, etc.), together with a substantial amount of auxiliary equipment typified by pumps, collection vessels, vacuum generating equipment, etc.
Such operations are characterized by high operating costs-principally costs of heating and cooling--plus pumping, etc.
Furthermore the properties of the materials being separated, as is evidenced by the distillation curves, may be such that a large number of plates may be required, etc. When the material forms an azeotrope with water, additional problems may be present which for example, could require that separation be effected in a series of steps (e.g. as in two towers) or by addition of extraneous materials to the system.
There are also comparable problems which are unique to adsorption systems.
It has been found to be possible to utilize membrane systems to separate mixtures of miscible liquids by reverse osmosis. In this process, the charge liquid is brought into contact with a membrane film; and one component of the charge liquid preferentially permeates the membrane. The permeate is then recovered as a liquid from the downstream side of the film.
Composite membranes prepared by interfacial crosslinking have been used in various processes including water purification, reverse osmosis, organic/organic separations, gas/liquid separation, etc. In such processes, the charge/retentate side of the membrane is commonly at a high pressure (typically 700 psig) and the permeate side of the membrane is commonly at atmospheric pressure The permeate is recovered in liquid phase.
Illustrative of such processes are those set fort in the following patents:
U.S. Pat. No. 5,037,555 to Texaco Inc as assignee of Mordechai Pasternak and Abraham Morduchowitz is directed to desalination of water by reverse osmosis across a membrane of a polyimine polymer which has been cross-linked with an isocyanate or a carbonyl chloride cross-linking agent.
U.S. Pat. No. 4,865,745 to Texaco Inc as assignee of Mordechai Pasternak is directed to dewatering of dilute aqueous solutions of organic oxygenates by a pressure drive process across a membrane of a polyimine polymer which has been cross-linked with an isocyanate or a carbonyl chloride cross-linking agent.
U.S. Pat. No. 4,897,091 to Texaco Inc as assignee of Mordechai Pasternak and Richard Beaupre is directed to separation of carbon dioxide from solution thereof in methanol by use in a pressure driven process, of a membrane which is the reaction product of (i) a polyamine and (ii) a polyisocyanate or a poly (carbonyl chloride).
U.S. Pat. No. 4,985,138 to Texaco Inc as assignee of Mordechai Pasternak is directed to separation of dewaxed oil from dewaxing solvent by a pressure driven process across a polyurea membrane.
There is also a body of prior art directed to separation of water from dilute solutions of various compositions by pervaporation wherein the permeate is recovered in vapor phase under vacuum. Illustrative of such processes are those set forth in the following patents:
U.S. Pat. No. 4,802,988 to Texaco Inc as assignee of John Reale, Jr. and Craig R. Bartels is directed to separation of water from ethylene glycol by pervaporation across a membrane of polyvinyl alcohol which has been cross-linked with an aliphatic polyaldehyde containing at least three carbon atoms.
U.S. Pat. No. 5,004,861 to Texaco Inc as assignee of Mordechai Pasternak, Craig R. Bartels, and John Reale, Jr. is directed to separation of water from a charge mixture of hydrocarbon and organic oxygenate by use, in a pervaporation process, of (i) a membrane of polyvinyl alcohol which has been cross-linked with a polyaldehyde containing at least three carbon atoms or (ii) a composite membrane of blended polyvinyl alcohol and polyacrylic acid.
U.S. Pat. No. 4,935,144 to Texaco Inc as assignee of Mordechai Pasternak, Craig R. Bartels, and John Reale, Jr. is directed to separation of aqueous solutions of organic oxygenates by pervaporation across a membrane of polyvinyl alcohol which has been cross-linked with a polyaldehyde containing at least three carbon atoms.
U.S. Pat. No. 4,910,344 to Texaco Inc as assignee of Mordechai Pasternak, Craig R. Bartels, and John Reale, Jr. is directed to separation of water from a charge mixture of hydrocarbon and organic oxygenates by pervaporation across a composite membrane of polyvinyl alcohol and a polyarcylic acid.
U.S. Pat. No. 4,992,176 to Texaco Inc as assignee of Craig R. Bartels is directed to dehydration of organic oxygenates by pervaporation through a membrane of dibromo butane-cross-linked polyvinyl pyridine.
U.S. Pat. No. 5,032,278 to Texaco Inc as assignee of John Reale, Jr. is directed to dehydration of hydrocarbon/organic oxygenate mixtures by pervaporation across a heat-treated polyethylene imine membrane.
Additional background may be obtained from (i) U.S. Pat. No. 4,411,787 to UOP as assignee of Riley; (ii) J. E. Cadotte et al, J. Macromol. Sci-Chem A15 (5) p 727 (1981); (iii) L. T. Rozelle et al Chapter 12 in Reverse Osmosis and Synthetic Membranes S. Sourirajan (Ed). See also the references cited in the above patents.
It is an object of this invention to provide a process for dewatering aqueous solutions. Other objects will be apparent to those skilled in the art.